Resin foams typified by a rigid urethane foam, a flexible urethane foam and expanded polystyrene are being used as heat insulating materials of houses and the like, and they play a very important role in reducing energies for cooling and heating under increasing energy conservation minds in recent years.
Such heat insulating materials exhibit excellent thermal insulation performance generally by containing low thermal conductivity gas in a very small volume inside a resin foam.
As the low thermal conductivity gas in heat insulating materials in past years, chlorofluorocarbons (CFC) were widely used, but because CFC are a substance destroying the ozone layer, in place of them, hydrofluorocarbons (HFC) and low molecular hydrocarbons such as butane and propane have been being used (JP 2007-332203 A and WO 00/01761 A1). However, since HFC have a very large Global Warming Potential, and the low molecular hydrocarbons are inflammable, there is arising a movement that carbon dioxide of lower environmental load and more safety is used.
However, since carbon dioxide is inferior in thermal insulation performance to HFC and low molecular hydrocarbons, to obtain thermal insulation properties of excellent thermal insulation performance, it is necessary to improve thermal insulation performance of foam itself.
In general, the thermal insulation performance of foam varies depending on porosity (X) and bubble diameter except for low thermal conductivity gas contained inside. The larger the porosity (X) and the smaller the bubble diameter, the higher the thermal insulation performance is exhibited. In the conventional art, to make porosity (X) large, the only measure was to make bubble diameter large, so there was a tendency that the thermal insulation performance became bad when more than a certain porosity (X).
Thus, in recent years, various studies have been done for controlling the bubble structure of foam. Particularly in JP 2007-153964 A, it is shown that various bubble diameters can be produced by using a styrene resin as a base and two kinds of blowing agents (water and carbon dioxide).
However, because the overall bubble size is large, no good thermal insulation performance can be obtained. Since water is used as a blowing agent, it will be a technique hardly applicable to polyester resins that hydrolysis is concerned.
It could therefore be helpful to provide a resin foam excellent in thermal insulation performance and environmental performance, further, to provide a non Freon thermal insulation foam material maintaining the excellent thermal insulation performance for a long period of time and not generating condensation easily.